1. Field of the Invention
This invention relates generally to magnetic heads and methods of making the same, and more particularly to read sensors and methods of making the same using an etch-stop layer between the capping layer and the free layer so that when portions of the capping layer are removed via a reactive ion etch (RIE), damage to the free layer that would otherwise occur is reduced or eliminated.
2. Description of the Related Art
Computers often include auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic heads including read sensors are then used to read data from the tracks on the disk surfaces.
In high capacity disk drives, magnetoresistive read sensors, commonly referred to as MR heads, are the prevailing read sensors because of their capability to read data from a surface of a disk at greater linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an “MR element”) as a function of the strength and direction of the magnetic flux being sensed by the MR layer.
The conventional MR sensor operates on the basis of the anisotropic magnetoresistive (AMR) effect in which an MR element resistance varies as the square of the cosine of the angle between the magnetization in the MR element and the direction of sense current flow through the MR element. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the MR element, which in turn causes a change in resistance in the MR element and a corresponding change in the sensed current or voltage.
Another type of MR sensor is the giant magnetoresistance (GMR) sensor manifesting the GMR effect. In GMR sensors, the resistance of the MR sensing layer varies as a function of the spin-dependent transmission of the conduction electrons between magnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and non-magnetic layers and within the magnetic layers.
GMR sensors using only two layers of ferromagnetic material (e.g., Ni—Fe) separated by a layer of non-magnetic material (e.g., Cu) are generally referred to as spin valve (SV) sensors manifesting the GMR effect (also referred to as the SV effect). In an SV sensor, one of the ferromagnetic layers, referred to as the pinned layer, has its magnetization typically pinned by exchange coupling with an antiferromagnetic (e.g., NiO or Fe—Mn) layer. The magnetization of the other ferromagnetic layer, referred to as the freelayer, however, is not fixed and is free to rotate in response to the field from the recorded magnetic medium (the signal field). In the SV sensor, the SV effect varies as the cosine of the angle between the magnetization of the pinned layer and the magnetization of the freelayer. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in direction of magnetization in the freelayer, which in turn causes a change in resistance of the SV sensor and a corresponding change in the sensed current or voltage.
FIG. 1 shows a prior art SV sensor 100 comprising end regions 104 and 106 separated from each other by a central region 102. A freelayer (free ferromagnetic layer) 110 is separated from a pinned layer (pinned ferromagnetic layer) 120 by a non-magnetic, electrically-conducting spacer 115. The magnetization of the pinned layer 120 is fixed by an antiferromagnetic (AFM) layer 125. Freelayer 110, spacer 115, pinned layer 120 and the AFM layer 125 are all formed in the central region 102. Hard bias layers 130 and 135 formed in the end regions 104 and 106, respectively, provide longitudinal bias for the freelayer 110. Leads 140 and 145 formed over hard bias layers 130 and 135, respectively, provide electrical connections for the flow of the sensing current Is from a current source 160 to the MR sensor 100. Sensing means (a detector) 170 connected to leads 140 and 145 senses (detects) the change in the resistance due to changes induced in the freelayer 110 by the external magnetic field (e.g., field generated by a data bit stored on a disk).
Another type of SV sensor is an antiparallel (AP) pinned SV sensor. In AP-pinned SV sensors, the pinned layer is a laminated structure of two ferromagnetic layers separated by a non-magnetic coupling layer such that the magnetizations of the two ferromagnetic layers are strongly coupled together antiferromagnetically in an antiparallel orientation. The AP-pinned SV sensor provides improved exchange coupling of the antiferromagnetic (AFM) layer to the laminated pinned layer structure than is achieved with the pinned layer structure of the SV sensor of FIG. 1. This improved exchange coupling increases the stability of the AP-pinned SV sensor at high temperatures which allows the use of corrosion resistant antiferromagnetic materials such as NiO for the AFM layer.
FIG. 2 shows a prior art AP-pinned SV sensor 200 comprising end regions 204 and 206 separated from each other by a central region 202. A freelayer 210 is separated from a laminated AP-pinned layer structure 220 by a nonmagnetic, electrically-conducting spacer layer 215. The magnetization of the laminated AP-pinned layer structure 220 is fixed by an AFM layer 230. The laminated AP-pinned layer structure 220 comprises a first ferromagnetic layer 222 and a second ferromagnetic layer 226 separated by an antiparallel coupling (APC) layer 224 of nonmagnetic material. The two ferromagnetic layers 222, 226 (PF1 and PF2) in the laminated AP-pinned layer structure 220 have their magnetization directions oriented antiparallel, as indicated by the arrows 223, 227 (arrows pointing into and out of the plane of the paper respectively). The AFM layer 230 is formed on a seed layer 240 deposited on the substrate 250. To complete the central region 202 of the SV sensor, a capping layer 205 (e.g., tantalum) is formed on the freelayer 210. Some conventional read sensors utilize a layer of copper-oxide (CuO) in between the capping layer and the free layer to improve sensor performance. Hard bias layers 252 and 254 formed in the end regions 204 and 206, respectively, provide longitudinal bias for the freelayer 210. Leads 260, 265 provide electrical connections for the flow of the sensing current Is from a current source 270 to the SV sensor 200. Sensing means 280 connected to leads 260, 265 senses the change in the resistance due to changes induced in the freelayer 210 by the external magnetic field (e.g., field generated by a data bit stored on a disk).
As apparent, multiple thin film layers are patterned to form various shaped layers in the head. Some of these layers are plated while other layers are sputter deposited on a wafer substrate. The read head portion of a magnetic head assembly includes multiple layers that are typically sputter-deposited. For example, the multiple layers of a read sensor, hard bias and lead layers connected to the read sensor, and first and second read gap layers below and on top of the read sensor are typically sputter deposited.
One prior art method of forming shaped sputter deposited layers is to sputter deposit a full film layer of the required material on a wafer substrate, form a patterned photoresist layer on the layer, ion mill away the exposed portion of the layer and then remove the photoresist layer leaving the desired shaped layer that was protected therebelow. This first conventional method of shaping sputter deposited layers has been generally superseded by a second conventional method which utilizes a bilayer lift-off mask scheme.
The lift-off mask used in the second conventional method has a T-shape (as seen in cross-section) wherein the vertical portion of the T is short and wide but less wide than the horizontal top portion of the T. The top portion of the T is generally a patterned photoresist layer and the bottom vertical portion of the T is a release layer. This configuration provides left and right undercuts (as seen in cross-section) wherein each undercut has a height and a length below the top photoresist portion. In this method, the lift-off mask is employed for the purpose of making contiguous junctions (CJs) of the left and right lead layers with left and right side edges respectively of the read sensor.
Multiple read sensor layers are sputter deposited in full film on the wafer substrate followed by formation of the lift-off mask covering a read sensor site. Ion milling is then employed to remove all of the read sensor material except that below the mask. Full films of hard bias and lead layer materials are then sputter deposited which cover the top of the lift-off mask and an area surrounding the lift-off mask. It is important that the height and length of the undercuts is sufficient such that a photoresist stripper can reach the bottom release layer. The stripper is then introduced to dissolve the bottom release layer after the hard bias and lead layer depositions. This causes the lift-off mask and the hard bias and lead materials deposited thereon to be released from the wafer substrate leaving the aforementioned contiguous junctions between the left and second right layers and the left and right side edges respectively of the read sensor.
Several variations of this method are being developed. Two main approaches are an Exchange Tabs (ET) technique and a Lead Overlay (LOL) technique. In the ET technique, an exchange biasing “tab” is basically placed on both sides of the GMR sensor's free layer to define the magnetic track width of the sensor. To begin, a GMR film is deposited and then a lift-off mask is formed in a central region over the GMR film. With the lift-off mask in place, the capping layer (e.g. tantalum) and part of the free layer are etched in end regions which surround the central region. Next, left and right exchange layers are deposited together in the end regions which is followed by the deposition of left and right lead layers. Deposition of the left and right exchange layers may be preceded by the deposition of left and right ferromagnetic layers. The lift-off mask is subsequently removed to thereby form the read sensor.
In the LOL technique, a first lift-off mask is formed in the central region over the GMR layers and sensor materials not protected by the lift-off mask are removed. Left and right hard bias layers are then deposited together in the end regions (optionally with a capping layer). Next, the first lift-off mask is removed, and a second lift-off mask having a narrower structure than the first is formed in the central region. Those portions of the sensor that are exposed (e.g. top edges of the sensor's tantalum capping layer) are slightly etched to remove any tantalum-oxide (TaOx) or other highly resistive material on top of the sensor. The oxide is undesirably formed due to the exposure to open air and annealing processes used. Left and right lead layers are then deposited in the end regions. A read sensor is formed such that edges of the left and the right lead layers are positioned on top of the edges of the sensor to define the magnetic track width.
In each one of these techniques, it is necessary to remove a portion of the capping layer without causing damage to the underlying sensor ferromagnetic material. Furthermore, this removal needs to be done at the junction area which is heavily shadowed by the lift-off mask structure.
It has been observed that physical ion milling is not ideal for this task since long “tails” of the capping layer remain in the junction area even though they are removed in the field area. On the other hand, it has been observed that an etching mechanism such as reactive ion etching (RIE) desirably exhibits selectivity between the capping layer (Ta/TaOx) and the underlying ferromagnetic material. Thus, the RIE appears to be particularly suited for this application. However, a RIE with fluorine chemistry undesirably causes damage to the underlying free layer. FIG. 3 is a graph 300 which shows the free layer moment loss vs. capping layer etch time. As apparent, the free layer moment loss dramatically increases as the etching time increases.
Accordingly, there is a resulting need for a method and device which cause little or no damage to the underlying free layer when portions of the capping layer are removed via etching.